The term metal fatigue refers to gradual degradation and eventual failure that occur under loads which vary with time, and which are lower than the static strength of the metallic specimen, component or structure concerned. The static strength is the load which causes failure in one application. The loads responsible are called fatigue loads. These loads are cyclic in nature, but the cycles are not necessarily all of the same size or clearly discernible. A fatigue load in which individual cycles can be distinguished is sometimes called a cyclic load.

Metal fatigue is largely a descriptive subject, and as such it has accumulated an enormous literature (Pook 1983a). Nevertheless, the basic concepts needed for an understanding of the metal fatigue literature are reasonably straightforward, and these are described in this book. The descriptions can be divided into two groups, metallurgical and mechanical. Metallurgical descriptions are concerned with the state of the metal before, during and after the application of fatigue loads, and are usually taken to include the study of metal fatigue mechanisms. Mechanical descriptions are concerned with the mechanical response to a given set of loading conditions, for example the number of load cycles needed to cause failure. Mechanical descriptions are more useful from an engineering viewpoint, where service behaviour must be predicted, and are therefore given more emphasis in this book.

Rigorous definition of exactly what is meant by metal fatigue is difficult and not particularly helpful for its understanding. An early...